Soil Chemistry and Pollution
Zahra Albozahar; Neda Moradi; ُSaeid Hojati
Abstract
Introduction: Today, water consumption has increased dramatically as a result of technological advancement, extraordinary industrial development and urbanization, which has caused the production of large amounts of toxic waste. Zinc (Zn) is an essential element for plants and humans, however, excessive ...
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Introduction: Today, water consumption has increased dramatically as a result of technological advancement, extraordinary industrial development and urbanization, which has caused the production of large amounts of toxic waste. Zinc (Zn) is an essential element for plants and humans, however, excessive concentrations of zinc can cause problems for humans such as abdominal pain, nausea and vomiting. Zinc is the most toxic pollutant that enters the aquatic system through industrial wastewater. World health organization (WHO) has recommended limit concentration of zinc in drinking water of 5.0 mg L-1. Adsorption is one of the most efficient ways to remove heavy metals from the environment. Clay minerals are one of the good adsorbents for the adsorption of heavy metals due to their large surface areas, high ion exchange capacity and layered structure. Some factors such as temperature, pH, size of adsorbent, type of adsorbent and amount of adsorbent are considered as important factors in controlling the behavior of heavy metals in aqueous solution. The temperature of the solution can increase or decrease the adsorption of elements, which indicates the exothermic or exothermic nature of the surface adsorption reaction. Therefore, this research was carried out with the aim of investigating the effect of temperature on the kinetics and thermodynamics of Zn removal using sepiolite and kaolinite minerals.Materials and Methods: In this research, two clay minerals (kaolinite and sepiolite) in a size of 25-53 µm were used as zinc metal adsorbents. Sepiolite mineral was collected from mines in Fariman region of Razavi Khorasan province and kaolinite was collected from Lalejin in Hamadan province. The kinetics and thermodynamics of Zn absorption from aqueous solutions by sepiolite and kaolinite were investigated. For kinetic studies, 0.1 g of sepiolite and kaolinite adsorbent was poured into a centrifuge tube and 20 ml of Zn solution with a concentration of 50 mg L-1 of zinc nitrate background solution was added to it and at different times (5, 10, 15, 20, 30, 60, 120, 240, 480, 720, 1440 and 2880 minutes) was stirred. The experiment of adsorption kinetics was performed at pH 5 and at a temperature of 25 ± 1 °C. The thermodynamics of zinc adsorption was investigated at temperatures of 25, 35 and 45 ℃. The adsorption behavior of zinc metal by sepiolite and kaolinite minerals was evaluated at different times with pseudo-first-order, pseudo-second-order, Ilovich and intraparticle diffusion kinetic models through non-linear regression and using Solver software. Then, the thermodynamic parameters of adsorption process including: the activation energy (Ea), gibbs free energy (ΔG), entropy (ΔS) and enthalpy (ΔH) were determined.Results and Discussion: The results of this research showed that by increasing the contact time and decreasing the temperature of the solution from 45 to 25 ℃, the amount of Zn adsorption by both minerals increased. Also, the equilibrium time was determined to be 720 minutes. The results showed that the adsorption efficiency decreases with increasing temperature and the highest removal percentage was observed at 25 ℃. Based on the results obtained from the fitting of kinetic models with experimental data, the pseudo-second order model with the highest explanatory coefficient (R2=0.99) was selected as the best model. Adsorption capacity (qe) of Zn estimated from the pseudo-second order model for sepiolite and kaolinite at 25℃ compared to 45℃ decreased by 44.30 and 38.19%, respectively. Also, the amount of Zn adsorption capacity for sepiolite mineral was higher than kaolinite. The activation energy (-9.79 to -23.81 kJ mol-1) revealed the physical adsorption of Zn by sepiolite and kaolinite. The activation energy of Zn adsorption onto the sepiolite (-23.81 kJ mol-1) and Kaolinite (-9.79 kJ mol-1) indicated that Zn was more strongly sorbed by sepiolite than kaolinite. Conclusion: the results obtained showed that sepiolite and kaolinite can be used an adsorbed to remove Zn from aqueous solution with good efficiency and low cost, while sepiolite had higher Zn adsorption capacity compared to kaolinite. Adsorption of Zn decreased with increasing temperature. The optimal temperature in this study for maximum adsorption of Zn by sepiolite and kaolinite was 40℃. Thermodynamic parameters including changes in Gibbs free energy (ΔG), enthalpy (ΔH) and entropy (ΔS) showed that zinc adsorption process by the studied minerals is an exothermic and spontaneous reaction. As a conclusion, sepiolite has a high potential for remove of Zn from wastewater.
Soil Chemistry and Pollution
Khosro Betyar; Neda Moradi; Abdolamir Moezzi; Shila Khajavi-Shojaei
Abstract
Introduction Phosphorus deficiency is one of the major problems of calcareous soils and a limiting factor for crop production in these soils and excessive use of phosphate fertilizers can cause pollution in soil and water. The use of organic amendments such as compost, biochar or a combination of them ...
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Introduction Phosphorus deficiency is one of the major problems of calcareous soils and a limiting factor for crop production in these soils and excessive use of phosphate fertilizers can cause pollution in soil and water. The use of organic amendments such as compost, biochar or a combination of them can be effective in improving the amount of available phosphorus of the soil. For this purpose, the effect of combined application of compost and biochar of sugarcane bagasse on phosphorus sorption and desorption were investigated.Materials and Methods Sugarcane bagasse and compost were provided from Debal Khozaei agro-industry Company. The oven-dried sugarcane bagasse 105 ºC were pass through 2 mm sieve and slow pyrolysed at 500 ºC using a laboratory muffle furnace with a heating rate of 5 ºC min-1 and presence of N2 flow to provide an anoxic condition. Some physico-chemical properties of samples were determined. The soil sample was collected from 0-30 cm of the campus of Shahid Chamran University of Ahvaz, Ahvaz, Khuzestan province, SW Iran (48° 65′91.12′′E31°30′53.82′′N). The studied soil classified as a Typic Haplocalcids. The air-dried soil samples were sieved (˂ 2 mm) and used for physico-chemical analysis. The incubation experiment was conducted with 7 treatments. The treatments including (1) control (without any amendments), (2) 100% sugarcane bagasse, (3) 100% sugarcane bagasse compost, (4) 100% sugarcane bagasse biochar, (5) 50% compost +50% biochar, (6) 75% compost + 25% biochar, (7) 25% compost + 75% biochar were added as 2% w/w to soil. The 200 g air-dried soil and treatments were mixed and kept in poly-ethylene containers for 120 days. Samples were incubated in 25 2 ºC and soil moisture was adjusted to soil field capacity using distilled water during the incubation time. At the end of incubation time, soil phosphorus sorption isotherm was measured. A 2.5 g of each treatment was transferred to a 50 ml centrifuge tube. Then, a 25 mL of CaCl2 0.01 M containing 0, 10, 20, 40, 60, 80, and 100 mg P L-1 (prepared from KH2PO4) was added to each centrifuge tube. Two drops of chloroform were added to each centrifuge tube to inhibit microbial growth. Samples were equilibrated at 25 1 ºC for 24 h on shaker at 150 rpm, and then centrifuged for 5 min at 3000 rpm and pass through 0.45-μm filter paper. The phosphate desorption was conducted on soil remaining in the filter immediately after sorption experiment. For this purpose, each treatment was resuspended with 25 ml of CaCl2 0.01 M solution without phosphate and shaken for 24 h. after collecting the supernatant, desorbed phosphate was measured. For assessing the adsorbed phosphate, the difference between the initial phosphate concentration and the phosphate concentration at equilibrium was calculated. The Langmuir, Freundlich and temkin isotherm models were used to describe the sorption of phosphate. In addition, some phosphorus buffering indices including maximum buffering capacity (MBC), standard buffering capacity (SBC), equilibrium buffering capacity (EBC) and standard phosphorus requirement (SPR) were obtained from P sorption equations at 0.2 mg P L-1 concentration in soil solution. The experimental data were fitted by Microsoft Excel-SOLVER and graphs were plotted by Microsoft Excel.Results and Discussion The soil was had loam texture, with low SOC content and high pH and calcium carbonate content, also the results of the characteristics of sugarcane bagasse compost and biochar showed that the compost had high salinity and the biochar had high pH and C/N ratio. The amount of phosphorus absorption increased with increasing the initial concentration of phosphorus in the treated soils. The highest and lowest amount of phosphorus absorption were in the control in compost treatments, respectively. In general, different levels of biochar and compost treatments caused a decrease in phosphorus absorption compared to the control treatment. The results showed that P sorption and desorption are described well by the Freundlich and Langmuir equations with a high correlation coefficient; however, the Temkin equation described the P sorption and desorption in the soils poorly. Biochar and compost treatments significantly decreased the Freundlich n parameter. Results showed that the effects of compost and 75% compost + 25% biochar were significantly greater than the effects of other treatments on the n parameter exponential adsorption equation. Application of different treatments of sugarcane bagasse compost and biochar application caused a significant increase in MBC (25.4-70.7%) and EBC (33.1-69.4%). The standard P requirements (SPR) were lower in soils treated than in control soil.Conclusion The results showed that the combined application of biochar-compost of sugarcane bagasse reduced the sorption and increased desorption of phosphorus. The maximum buffering capacity (MBC) and equilibrium buffering capacity (EBC), standard buffering capacity (SBC) and standard phosphorus requirement (SPR) in compost and compost 75% + biochar 25% showed more decrease than the control. In general, the results of this study indicate that the combined application of biochar-compost of sugarcane bagasse reduces phosphorus sorption in soil in calcareous soils, which can increase the availability phosphorus for plants.
Soil Chemistry and Pollution
Neda Moradi; Mir Hassan Rasouli-Sadaghiani
Abstract
Introduction Recently, due to the enhancement of industrialization, urbanization, and disposal of wastes, fertilizers, and pesticides the concentration of heavy metals in agricultural soil has increased. Heavy metals are a serious threat to the environment due to their hazardous effects. Heavy metal ...
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Introduction Recently, due to the enhancement of industrialization, urbanization, and disposal of wastes, fertilizers, and pesticides the concentration of heavy metals in agricultural soil has increased. Heavy metals are a serious threat to the environment due to their hazardous effects. Heavy metal contamination of the soil is of particular attention due to food security issues and several reported health risks to both human and living organisms. In addition, large areas worldwide are polluted by lead (Pb). One of the major problems in the process of Phytoremediation is the low solubility of heavy metals, such as lead in the contaminated soil. Phytoextraction is a solar-driven remediation technology which greatly reduces the costs and has minimum adverse side effects. Lead (Pb) is among the highly toxic and most common heavy metals at contaminated sites. It originates from various anthropogenic sources and causes a variety of health, environmental, and ecological problems. The weed plant species are usually of the quickly growing nature and have higher biomass under unfavorable environments. Their phytoremediation potential could be more effective in reducing food chain contamination and consequently the risk to human health. Therefore, the objective of this study was to assess the Pb remediation potential of Artemisia (Artemisia absinthium L.) and Xanthium (Xanthium strumarium L.) in contaminated calcareous soil. Materials and Methods This study was carried out under a greenhouse condition as a factorial experiment based on a randomized complete block design with two factors, including Pb concentration in four levels (0, 250, 500, and 1000 mg Pb kg-1 soil) and plant type in two levels of Artemisia (Artemisia absanthium L.) and Xanthium (Xanthium strumarium L.) and in three replications. In this study, the soil was selected and was spiked with 0, 250, 500, and 1000 mg Pb kg−1 soil. Then plants were grown in pots containing the contaminated soil. At the end of the growth period, the dry weight of root and shoot, Pb concentration in the root and shoot of plants, and soil bioavailable Pb were measured. Also, the tolerance index (TI) of root and shoot was calculated by dividing the dry biomass of plant in each treatment by dry biomass in the control treatment at Pb0 mg kg-1 of the soil. Moreover, the stabilized Pb in roots (MS) and extracted Pb by shoots (ME) were calculated. For evaluating the ability of plants on uptake and shoot and root accumulation of Pb, mBCF (Modified bioaccumulation factor) and mBAF (bioconcentration factors) of shoot and root were calculated by dividing the Pb concentration in plant dry matter to bioavailable Pb concentration in soil and dividing the Pb accumulation in the plant fraction bioavailable metal content in the soil. In addition, the modified translocation factor (mTF) was calculated by dividing the Pb concentration in shoot dry matter by Pb concentration in root dry matter. Results and Discussion Results of this study indicated that with increasing soil Pb contamination, the root and shoot dry weight and tolerance index of plants decreased, while shoot and root Pb concentration, stabilized Pb in roots and the extracted Pb from shoots increased. The highest and lowest relative shoot and root dry weight were observed in Pb0 and Pb1000 treatments, respectively. There was no significant difference in the tolerance index (TI) of plants. In this study, roots and shoots mBCF, obtained for both plants and different levels of Pb in soil, were above unity, indicating that the plant is able to take up and accumulate Pb. A. absanthium PGPR had higher mTF than X. strumarium plant at every concentration of soil Pb. The assessment of the phytoremediation performance clearly revealed that the amounts of all phytoextraction indices in A. absanthium were higher than X. strumarium, while all phytostabilization indices in X. strumarium were higher than X. strumarium. In general, maximum Pb accumulation for root was recorded for X. strumarium (average of root mBAF, mBCF, and mTF 1.65 %, 5.48 and 0.97, respectively) and maximum accumulation of Pb in shoot was observed for A. absantium (average of shoot mBAF, mBCF, and mTF 2.79 %, 2.86, and 1.84, respectively). Conclusion It could be concluded that X. strumarium and A. absanthium, with high biomass in native condition, might be effective in phytostabilization and phytoextraction of Pb, respectively, especially in low levels of soil Pb contamination (250 and 500 mg kg-1).
